Every eye has a small area on the retina where no light receptors exist, called the blind spot. You can prove it by drawing a dot and a plus sign on paper, closing one eye, and slowly moving the paper toward your face. At a certain distance, the dot disappears because it falls on your blind spot.

The light-sensing layer at the back of your eye has one small area with no light receptors at all — and you can find it yourself. Draw a small dot and a plus sign about six inches apart on paper. Close one eye and focus on the plus sign. Slowly move the paper toward your face. At a certain distance, the dot disappears. That is the moment it falls on the blind spot, where the optic nerve exits the retina and leaves no room for receptors.